Carp, now I can't remember when that changed. That was the behavior ages ago, and then I think you're right that there was an implicit defined-ness check stuck in sometime. I want to say I hit that with an older (5.6 era) perl sometime recently but I can't reproduce it with 5.6.1.

Probably just best to remember it can happen in case you're ever messing around with a really old version, and not worry about it otherwise.